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Your answer is correct, but gives the wrong impression that it is used only in a few minor dialects (such as Gunma and Saitama dialects). It is in fact used in most of the kansai dialects, and the western part of Japan. Also, it is better to describe the relation between ん and の (deletion of the vowel).
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user458Dec 26 '11 at 6:45

if you wanted to end with just ん without the です you should probably just use the informal of んです which is の

明日学校にいくの？
明日学校に行かないと思う、、、風邪引いたの。

ん like tsuyoshi said, is a dialect version of の seen in various regions of Japan. While it doesn't seem to be used in Aichi, all of my co-workers know of it. So it could be said that you can use it and you will be understood, but it is definately not standard japanese.

I can't think of one time I have heard that...Not to say it hasn't happened. Using the whole んです smoothly was stressed at school, as it makes your Japanese sound really natural. So I think I would notice if I heard someone end on the ん...I would stick to the normal usage until you hear a native speaker use it the way your friend did.